The present invention relates to a process for converting a high-boiling hydrocarbon feedstock into lighter boiling hydrocarbon products. More in detail, the present invention relates to a process for converting hydrocarbons, especially hydrocarbons originating from refinery operations, such as for example atmospheric distillation unit or a fluid catalytic cracking unit (FCC), into lighter boiling hydrocracked hydrocarbons having a boiling point of cyclobutane and lower.
U.S. Pat. No. 4,137,147 relates to a process for manufacturing ethylene and propylene from a charge having a distillation point lower than about 360 DEG C. and containing at least normal and iso-paraffins having at least 4 carbon atoms per molecule, wherein: the charge is subjected to a hydrogenolysis reaction in a hydrogenolysis zone, in the presence of a catalyst, (b) the effluents from the hydrogenolysis reaction are fed to a separation zone from which are discharged (i) from the top, methane and possibly hydrogen, (ii) a fraction consisting essentially of hydrocarbons with 2 and 3 carbon atoms per molecule, and (iii) from the bottom, a fraction consisting essentially of hydrocarbons with at least 4 carbon atoms per molecule, (c) only the fraction consisting essentially of hydrocarbons with 2 and 3 carbon atoms per molecule is fed to a steam-cracking zone, in the presence of steam, to transform at least a portion of the hydrocarbons with 2 and 3 carbon atoms per molecule to monoolefinic hydrocarbons; the fraction consisting essentially of hydrocarbons with at least 4 carbon atoms per molecule, obtained from the bottom of the separation zone, is supplied to a second hydrogenolysis zone where it is treated in the presence of a catalyst, the effluent from the second hydrogenolysis zone is supplied to a separation zone to discharge, on the one hand, hydrocarbons with at least 4 carbon atoms per molecule which are recycled at least partly to the second hydrogenolysis zone, and, on the other hand, a fraction consisting essentially of a mixture of hydrogen, methane and saturated hydrocarbons with 2 and 3 carbon atoms per molecule; a hydrogen stream and a methane stream are separated from the mixture and there is fed to the steam-cracking zone the hydrocarbons of the mixture with 2 and 3 carbon atoms, together with the fraction consisting essentially of hydrocarbons with 2 and 3 carbon atoms per molecule as recovered from the separation zone following the first hydrogenolysis zone. At the outlet of the steam-cracking zone are thus obtained, in addition to a stream of methane and hydrogen and a stream of paraffinic hydrocarbons with 2 and 3 carbon atoms per molecule, olefins with 2 and 3 carbon atoms per molecule and products with at least 4 carbon atoms per molecule.
U.S. Pat. No. 3,660,270 relates to a process for producing gasoline which comprises hydrocracking a petroleum distillate in a first conversion zone, separating the effluent from the first conversion zone into a light naphtha fraction, a second fraction having an initial boiling point between 180 and 280 F. and an end boiling point between about 500′ to 600 F., and a third heavy fraction, hydrocracking and dehydrogenating the second fraction in a second conversion zone in the presence of a catalyst and recovering from the second conversion zone at least one naphtha product.
US patent application No 2009/159493 relates to a method for hydroprocessing a hydrocarbon feedstock, said method employing multiple hydroprocessing zones within a single reaction loop, each zone having one or more catalyst beds. According to this method fresh feed is passed to the top of a fixed bed hydrotreater reactor. Hydrogen is added in between the first and second beds, and second and third beds of fixed bed hydrotreater reactor. The hydrotreated jet and diesel range material is recovered as liquid stream at high pressure and pumped to a hydrocracking reactor. Hydrogen is added in between the first and second beds and second and third beds of the hydrocracking reactor.
U.S. Pat. No. 5,603,824 relates to an integrated hydroprocessing method in which hydrocracking, dewaxing and desulfurization all occur in a single, vertical two bed reactor, wherein a distillate is split into heavy and light fractions, the heavy fraction being hydrocracked and partially desulfurized in the top reactor bed, and the effluent from the top bed is then combined with the light fraction and is cascaded into the bottom reactor bed, where dewaxing for pour point reduction and further desulfurization occurs.
Conventionally, crude oil is processed, via distillation, into a number of cuts such as naphtha, gas oils and residua. Each of these cuts has a number of potential uses such as for producing transportation fuels such as gasoline, diesel and kerosene or as feeds to some petrochemicals and other processing units.
Light crude oil cuts such as naphtha's and some gas oils can be used for producing light olefins and single ring aromatic compounds via processes such as steam cracking in which the hydrocarbon feed stream is evaporated and diluted with steam then exposed to a very high temperature (800° C. to 860° C.) in short residence time (<1 second) furnace (reactor) tubes. In such a process the hydrocarbon molecules in the feed are transformed into (on average) shorter molecules and molecules with lower hydrogen to carbon ratios (such as olefins) when compared to the feed molecules. This process also generates hydrogen as a useful by-product and significant quantities of lower value co-products such as methane and C9+ Aromatics and condensed aromatic species (containing two or more aromatic rings which share edges).
Typically, the heavier (or higher boiling point) aromatic rich streams, such as residua are further processed in a crude oil refinery to maximize the yields of lighter (distillable) products from the crude oil. This processing can be carried out by processes such as hydro-cracking (whereby the hydro-cracker feed is exposed to a suitable catalyst under conditions which result in some fraction of the feed molecules being broken into shorter hydrocarbon molecules with the simultaneous addition of hydrogen). Heavy refinery stream hydrocracking is typically carried out at high pressures and temperatures and thus has a high capital cost.
An aspect of the conventional hydrocracking of heavy refinery streams such as residua is that this is typically carried out under compromise conditions which are chosen to achieve the desired overall conversion. As the feed streams contain a mixture of species with a range of easiness of cracking this results in some fraction of the distillable products formed by hydrocracking of relatively easily hydrocracked species being further converted under the conditions necessary to hydrocrack species more difficult to hydrocrack. This increases the hydrogen consumption and heat management difficulties associated with the process, and also increases the yield of light molecules such as methane at the expense of more valuable species.
US patent application No's 2012/0125813, US 2012/0125812 and US 2012/0125811 relate to a process for cracking a heavy hydrocarbon feed comprising a vaporization step, a distillation step, a coking step, a hydroprocessing step, and a steam cracking step. For example, US patent application No 2012/0125813 relates to a process for steam cracking a heavy hydrocarbon feed to produce ethylene, propylene, C4 olefins, pyrolysis gasoline, and other products, wherein steam cracking of hydrocarbons, i.e. a mixture of a hydrocarbon feed such as ethane, propane, naphtha, gas oil, or other hydrocarbon fractions, is a non-catalytic petrochemical process that is widely used to produce olefins such as ethylene, propylene, butenes, butadiene, and aromatics such as benzene, toluene, and xylenes.
US patent application No 2009/0050523 relates to the formation of olefins by thermal cracking in a pyrolysis furnace of liquid whole crude oil and/or condensate derived from natural gas in a manner that is integrated with a hydrocracking operation.
US patent application No 2008/0093261 relates to the formation of olefins by hydrocarbon thermal cracking in a pyrolysis furnace of liquid whole crude oil and/or condensate derived from natural gas in a manner that is integrated with a crude oil refinery.